This invention relates to a bale opener for opening fiber bales which are supported in series and which contain cotton fiber, synthetic fiber or the like. The opening is effected by detaching fiber tufts from the upper face of the bales. The removed fiber tufts are conveyed pneumatically, for example, to a tuft blending apparatus. The bale opener has a tower structure mounted on a carriage movable on rails. The tower supports a horizontally projecting opening assembly which houses the detaching mechanism proper, formed, for example, of opening rollers. The tower is rotatable about a vertical axis through 180.degree. by means of a drive motor at the end of its path of travel.
According to the prior art, the drive means for rotating the tower about its vertical axis comprises an electrically brakable drive motor. The tower is rotated at a low speed because of its large mass. Particularly because of the significant lateral dimensions of the cantilevered opening assembly, the structure to be rotated has a large moment of inertia related to the axis of rotation. In order to ensure a gentle, shock-free rotary motion, the drive is designed for low rpm's. In this arrangement, three-phase shunt motors are used which are switched on and off and which are controlled by a control pulse for triggering rotation and by a limit switch actuated when the tower reaches its end position. The limit stops are blocking mechanisms; for effecting shock absorption, at the end of the rotation a pin projects into a fixed jaw. Such an arrangement is limited to small rpm's, requiring long periods of rotation. Since the time required for rotating the tower represents a non-productive period for the bale opener, slow tower rotations are disadvantageous in that they adversely affect the efficiency (output) of the machine. While at higher rotary speeds the lost time periods may be reduced, abrupt changes in the rotary speed expose the machine, particularly the driving and rotating elements, to disadvantageous stressing forces.